1. Field of the Invention
This invention relates to textile articles possessing antimicrobial properties and a method for their preparation.
2. Description of Related Art
Textile articles which have been treated to render such articles microbicidal to microorganisms coming in contact with the article are known in the prior art. Such articles include those made from paper, fibers, woven and non-woven textiles and like fabrics which are designed for use in environments such as hospitals, food processing plants, laboratories and other areas where maintenance of germ-free conditions is essential.
For example, U.S. Pat. No. 2,791,518 discloses a method of imparting microbicidal properties to articles such as textiles by immersing the article in a first aqueous solution containing a water-soluble basic nitrogen compound (ammonia) and a monovalent silver salt soluble in said solution, followed by a second immersion in a second solution containing a second salt capable of ion exchange with the silver salt such that a monovalent silver salt precipitate is formed within the article. The formed silver precipitate is sparingly water soluble and imparts microbicidal properties to the articles so treated.
Similarly, U.S. Pat. No. 5,271,952 discloses a method of treating fibers to render them electrically conductive as well as anti-bacterial comprising immersing the fibers in a bath comprising an aqueous solution of a source of divalent copper ions, a reducing agent, sodium thiosulfate and a source of iodide ions, whereby copper iodide is adsorbed into the fibers. Similar techniques for rendering fibers conductive or resistant to bacteria involving the use of copper compounds are disclosed in U.S. Pat. Nos. 4,410,593 and 5,458,906.
It has also been disclosed that materials such as chlorinated hydantions may be grafted to textiles for the purpose of imparting antimicrobial properties, ie Williams et al, 218th ACS National Meeting (1999) Abstracts, Cell 32; CandEN September 6, page 36. However, textiles so treated tend to suffer severe diminishment of antimicrobial properties after as few as 5 hours of laundering and are UV unstable over long durations of exposure.
The invention provides a fibrous textile article containing an antimicrobial agent selected from the group consisting of tetrasilver tetroxide and derivatives thereof interstitially deposited within said article, said agent present in said article in an amount sufficient to impart antimicrobial properties to said article.
The invention also provides a process for imparting antimocrobial properties to a fibrous textile article comprising:
a. providing an aqueous solution containing a water soluble silver salt;
b. contacting said article with said solution for a period of time sufficient to uniformly wet said article with said solution;
c. immersing said wetted article in a bath containing a second aqueous solution containing a strong alkali and a water soluble oxidizing agent and heating said bath for a period of time sufficient to interstitially precipitate tetrasilver tetroxide within said article; and
d. removing said article from said bath.
Textile articles prepared in accordance with this invention, particularly woven and non-woven hydrophilic fabrics, exhibit outstanding antimicrobial resistance with respect to pathogens such as bacteria, viruses, yeast and algae, are resistant to degradation upon exposure to sunlight (ultraviolet light) and maintain their excellent antimicrobial properties even after a number of launderings.
Imparting antimicrobial properties to fiber and its derived textile products is achieved in the instant invention by interstitial deposition of the molecular crystal compound tetrasilver tetroxide, i.e., silver (I, III) oxide. Said silver moiety is the subject of several patents. U.S. Pat. No. 5,336,499, the disclosure of which is incorporated herein by reference, describes the anti-pathogenic properties of said silver oxide of formula Ag4O4 and also the mechanism of operation of the molecular device, based on a unique crystal having two monovalent silver (Ag I) ions and two trivalent silver (Ag III) ions in the molecule. The mechanism of killing pathogens described in the patent is based on the differential silver electronic activity between Ag (I) and Ag (III) resulting in electrocution of pathogens, followed by binding chelation of pathogenic surfaces.
U.S. Pat. No. 5,211,855 also discloses the use of Ag4O4 crystals to kill pathogens in utilitarian water bodies such as swimming pools.
An antimicrobial spectrum of Ag4O4 is to be found in a published article written by the instant inventor in the annual RandD issue of Soap Cosmetics Chemical Specialties 1994, 70, 3 p. 52-59 entitled xe2x80x9cSilver (II, III) Disinfectantsxe2x80x9d, shown in Table 1. The spectrum is based on specifications of the Association of Official Analytical Chemists (AOAC).
In said article, reference is made to the fact that monovalent silver is more anti-pathogenic than mercury which is more anti-pathogenic than copper, based on their oligodynamic activity as articulated by J. G. Horsfal in his xe2x80x9cPrinciples of Fungicidal Actionxe2x80x9d (Chronica Botanica 1956). The relative efficacy of metallic moieties against pathogens has been called the Horsfal series, and is as follows:
Ag greater than Hg greater than Cu greater than Cd greater than Cr greater than Ni greater than Co greater than Zn greater than Fe greater than Ca
The present inventor has found that with respect to a Horsfal series dedicated to silver, the relative efficacy against pathogens is as follows:
Ag4O4 greater than Ag(III) greater than Ag(II) greater than Ag(I)
The term xe2x80x9cfibrous textile articlexe2x80x9d as used herein is intended to encompass a wide variety of materials including paper, natural or synthetic fibers, threads and yarns made from materials such as cotton, rayon, wool, jute, nylon, polyesters, polyacetates, polyacrylics as well as cellulosics in general. More particularly, the term refers to fibers woven into a fabric such as knitting, and non-woven hydrophilic fabrics or webbing used in anti-pathogenic applications such as in the medical field, hospitals, biotechnology and food and dairy processing. Exemplary textile products of this genre include bandages, gauze, bandage pads, skin patches, work clothes (both disposable and reusable), bed sheets, masks, dust cloths, safety belts, surgical gowns, ambulance blankets, stretchers, filter materials, diapers, underwear, pajamas, video display terminal screens and the like.
For some antimicrobial applications, Ag4O4 crystals may be deposited within the interstices of fibrous articles by simply soaking the article in an aqueous dispersion of the crystals or by combining the crystals with a carrier medium and applying this composition to the fibrous article. This method of physical incorporation of the crystals is useful where the article is composed of low density or loosely associated fibers such as bandage pads, gauze pads and loosely non-woven products, and particularly laminated products wherein the treated fibrous article is subsequently sandwiched between one or two peelable layers which tend to keep the crystals trapped in the fibrous article until ready for use. Also, antimicrobial paper products may be made by simply mixing an aqueous dispersion of the Ag4O4 crystals with paper pulp prior to calendaring the pulp.
However, physical incorporation of the crystals is less effective where the treated article is a fiber or yarn or a higher density woven or non-woven fabric, since the pre-formed crystals can not sufficiently penetrate into the interstices of such articles. In such cases, deposition of Ag4O4 material via interstitial precipitation is preferred.
Interstitial precipitation of Ag4O4 material is accomplished by first providing an aqueous solution of a monovalent water soluble silver salt such as the nitrate perchlorate, acetate, methanesulfonate or fluoride, most preferably silver nitrate. Next the article to be treated, e.g., a fiber, yarn of a woven or non-woven fabric, is thoroughly wetted with this solution such that the article absorbs solution on fiber surfaces as well at one or more of the interstices between fibrils forming the fiber, between fibers forming the yarn or non-woven fabric, or between the weft and woof yarns present in woven fabrics. Wetting may be accomplished by uniformly spraying the article or more preferably by dipping the article in a bath of the silver salt solution for a period of time sufficient for the article to absorb the requisite amount of silver salt solution.
Next the wetted article is optionally squeezed to remove excess solution and immersed in a heated bath containing a second aqueous solution comprising a strong alkali and a water soluble oxidizing agent, and heated for a period of time sufficient to cause reaction leading to the interstitial precipitation of tetrasilver tetroxide (Ag4O4) crystal material in the interstices of the fibrous article. Suitable alkalis for this purpose include sodium or potassium hydroxide, with sodium hydroxide most preferred. Suitable oxidizing agents include alkali metal persulfates, permanganates or hypochlorites, but sodium and more preferably potassium persulfate is the preferred oxidizer. Reaction in the bath is accomplished by heating at a temperature of at least 85xc2x0 C., more preferably at least 90xc2x0 C. for a period of time sufficient to maximize yield of Ag4O4, generally from about 30 seconds to about 5 minutes. After the reaction is completed, the treated article is removed from the bath and may be washed several times with water to remove soluble inpurities or unreacted reagant.
The quantity of Ag4O4 material present in the resulting article will generally be a function of the quantity of silver salt sorbed by the article, which can vary depending on the nature of the article, e.g., loose vs. tight weave fabrics or whether the fiber is natural or synthetic, the former being more absorbtive of the silver salt solution.
In general, the quantity of alkali present in the second bath should be sufficient to maintain a strongly basic pH, i.e., about 13+, and providing a slight molar excess of silver salt over oxidizing agent is suitable to complete the reaction. Thus the content of tetrasilver tetroxide interstitially precipitated within any given fibrous article may be controlled by varying the concentration of the silver salt in the solution used to first wet the article and appropriately adjusting the quantities of alkali and oxidizing agent present in the immersion solution at approximately stoichiometric levels.
The term xe2x80x9cderivatives of Ag4O4xe2x80x9d is intended to include Ag4O4 reaction products prepared by reacting Ag4O4 with suitable water soluble acids to give the corresponding Ag (II) salts, e.g., reactions with fluoroboric acid or phosphoric acid to give the Ag (II) fluoroborate or phosphate, as disclosed in U.S. Pat. No. 5,107,295. Also included are divalent silver nitrate and divalent silver halides prepared by reacting Ag4O4 with nitric acid or the corresponding haloacids, e.g. HBr, HI or HCl as disclosed in U.S. Pat. No. 5,078,902. Trivalent silver derivatives such as Ag (III) biguanide prepared in accordance with U.S. Pat. No. 5,223,149 are also included.
Textile articles containing such derivatives would be prepared by further contacting the Ag4O4 containing article in an additional step with an aqueous solution containing up to stoichiometric amounts of the appropriate reagant(s) sufficient to convert at least a portion of the Ag4O4 to the Ag (II) or Ag (III) derivative.
Textile articles containing such derivatives are less preferred for the purposes of this invention because some derivatives may be generally more water soluble than Ag4O4, require a further processing step in their manufacture and are less effective as antimicrobial agents than Ag4O4 as shown in the silver Horsfal series described above. However, the Ag(II) or Ag(III) derivatives of Ag4O4 are useful as antimicrobial agents in fabrics which are designed for a single use such as bandages or disposable garments.
The content of the Ag4O4 or its derivatives (based on weight PPM silver) in the fabric may preferably range from as little as 0.5 weight PPM up to about 50,000 weight PPM, based on the weight of the textile article. The minimum content should be sufficient to kill pathogens from which protection is sought, whereas the maximum content is dictated by factors such as economy and affect on fabric properties. Generally speaking, the higher the silver content, the more effective will be the antimicrobial properties of the fabric. For most applications, silver content in the range of from about 30 to about 10,000 weight PPM will provide satisfactory antimicrobial properties.
Antimicrobial properties are evaluated in accordance with this invention using the Association of Official Analytical Chemists (AOAC) test method 972.04, which is used primarily to evaluate the bacteriostatic activity of laundry additive disinfectants. In this test, a square or rectangular sterile swatch of fabric is pressed into a petri dish containing a layer of nutrient agar which has been inoculated with a pathogen. Following a fixed period of incubation, each fabric sample is evaluated by measuring the clear zones adjacent the four sides of each test swatch as an index of antimicrobial activity. The presence of clear zones along all four sides of the swatch is indicative of antimicrobial activity, rated 4/4. The width of the clear zones in millimeters is reasonably indicative of the degree of antimicrobial activity.
The following examples are illustrative of the invention.